A telescope has a main mirror, also called primary mirror. The primary mirror concentrates the light rays to a secondary mirror which returns them to the focus of the telescope. The primary mirror must not be deformed under the effect of gravity for example. Often, a deformable intermediate mirror is used to correct the defects of the primary mirror. Also, the intermediate mirror is deformed by one or more actuators.
Modern telescopes are equipped with so-called “active” deformable optics. The mirror of such a telescope is therefore deformed permanently by actuators fixed directly on to the back of the mirror in order to always optimize the optical performance levels of the telescope.
To have a good resolution, the actuators have a floating head mounted on springs making it possible to divide the displacement of the actuator by a significant factor.
Nevertheless, the connection between the mirror and the floating head of the actuator poses several problems. First of all a significant integration defect generating a deformation of the mirror that cannot be corrected is regrettable. This is due to what is called parasitic torques. A poor alignment and guiding of the floating head by the springs can also occur, which causes parasitic torques to be injected when the actuator is operating to deform the mirror. Finally, upon launch, the launch imposes an additional stress requiring a rigid connection between the mirror and the actuators, significant moments and loads being generated on the mirror because of the offset additional masses borne by the mirror (notably the mass of the floating heads).